Two apparent loopholes
One: players disconnecting their wifi to leave games without penalty
Two: players running out the clock on other players by stalling in response to trade offers
I've had number two happen to me several times as well. I've disconnected from locked up games without penalty, although if there are two or three players left, whoever leaves last gets the win. A locked up game should be a washout from a scoring stand point, but then a locked up game shouldn't happen in the first place.
Two isn't really a loophole. The offering player can withdraw the offer at any time; she does not have to wait for responses from all other players.
I'll agree—better to say it introduces a strategy element that doesn't exist in the game it's meant to emulate. I'd suggest lengthening the timer, or slowing it while trades are considered.